The overall objective of this program is to support a multicenter case- control study on the potential etiologic factors for sarcoidosis. The cases will also be followed to gain information on the natural history of this disease including risk factors for progression of disease. A steering committee will develop a protocol and manual of operations which will address the most promising hypotheses to be pursued to identify the cause(s) of sarcoidosis. The protocol will include a comprehensive clinical characterization of each participant and determination of markers of immune responsiveness. Participation in a system for banking biological specimens will be required of each clinical center. The clinical coordinating center will collect, manage and analyze the data collected from the clinical centers. The clinical coordinating center will coordinate writing of the protocol and manual of operations, manage the logistics of the biological banking system, be responsible for setting up the data entry procedures and managing the database, be responsible for the logistics of the steering committee and Data and Safety Monitoring Board meetings, and perform the statistical analysis of the final data set. A six year schedule is envisioned as follows: Phase I (12 Months): A collaborative protocol and manual of operations will be developed; Phase II (48 Months): will involve the recruitment and follow-up of cases, patients and recruitment and interviewing of control subjects, and Phase III (12 Months): will involve data analysis.